Larus cachinnans

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3cy cachinnans: March

Phenotypic variation and systematics of Mongolian Gull

IN: Dutch Birding 23: 82, 2001 BY: Pierre Yésou

PART 1: INTRO & DISTRIBUTION
PART 2 PHENOTYPIC VARIATION

BELOW PART 3: BILL, EYE & LEG COLOUR

Bill colour

The bill is yellow, varying from pale yellow to bright orange-yellow, commonly with a paler tip. The red gonydeal spot usually does not reach the upper edge of the lower mandible, falling short by 2-3 mm. Dark markings (spots or broken lines in front of the red gonydeal spot) occur in one out of three birds. Of 107 adult-plumaged birds trapped at nests and examined in the hand, 17% showed dark markings on the upper mandible only and 15% on both mandibles (in one extreme case, the markings formed an almost complete dark bill band of c 3 mm width).

Mongolicus AL87 adult, May 26-28 2013, Telmen Nuur, Mongolia (48°49'N, 97°10'E). Picture: Andreas Buchheim.
Iris with limited speckling (1-5%). In Yésou's work this probably is "yellow (grey <10%)" (29% of the population).
Mongolicus AL69 adult, May 26-28 2013, Telmen Nuur, Mongolia (48°49'N, 97°10'E). Picture: Andreas Buchheim.
Iris with limited speckling (1-5%). In Yésou's work this probably is "yellow (grey <10%)" (29% of the population).
Mongolicus AL61 adult, May 26-28 2013, Telmen Nuur, Mongolia (48°49'N, 97°10'E). Picture: Andreas Buchheim.
Iris with limited speckling (5-10%). In Yésou's work this probably is "yellow (grey <10%)" (29% of the population).
Mongolicus AL89 adult, May 26-28 2013, Telmen Nuur, Mongolia (48°49'N, 97°10'E). Picture: Andreas Buchheim.
Iris with limited speckling (5-10%). In Yésou's work this probably is "yellow (grey <10%)" (29% of the population).
Mongolicus AL47 adult, May 26-28 2013, Telmen Nuur, Mongolia (48°49'N, 97°10'E). Picture: Andreas Buchheim.
Bird classified "pale eyed", iris is finely speckled (10-25%). In Yésou's work this probably is "yellowish (grey 10-50%)" (41% of the population).
Mongolicus AJ23 adult, June 2012, Khar Us Nuur, Mongolia (48°49'N, 97°10'E). Picture: Andreas Buchheim. What may seem to be a'pale eyed bird' in the field, is a bird with fine speckling when in the hand.
Mongolicus AL59 adult, May 26-28 2013, Telmen Nuur, Mongolia (48°49'N, 97°10'E). Picture: Andreas Buchheim.
Iris is marbled (10-25%). In Yésou's work this probably is "yellowish (grey 10-50%)" (41% of the population).
Mongolicus AL84 adult, May 26-28 2013, Telmen Nuur, Mongolia (48°49'N, 97°10'E). Picture: Andreas Buchheim.
Iris with dense speckling (75-99%). In Yésou's work this probably is "dark grey" (6% of the population).
Mongolicus AL55 adult, May 26-28 2013, Telmen Nuur, Mongolia (48°49'N, 97°10'E). Picture: Andreas Buchheim.
Iris is densely speckled (50-75%). In Yésou's work this probably is "pale grey (grey >50%)" (22% of the population).
Mongolicus AL43 adult, May 26-28 2013, Telmen Nuur, Mongolia (48°49'N, 97°10'E). Picture: Andreas Buchheim.
Bird classified "dark eyed", iris is densely speckled (75-99%). In Yésou's work this probably is either "dark grey" (6% of the population) or "brown" (2% of the population).

Eye colour

The orbital ring was vermilion-red in all adult-plumaged birds I examined in the hand. Pyzhianov & Tupitchyn (1992) described the iris as ranging from pale ashy-grey to olive-grey to dark smoky-grey. 54 and 68% of their samples of Lake Baikal and Lake Khubsugul, respectively, were pale eyed. They found no correlation be tween iris and leg colours (a point I did not check).


FIGURE 2 Variability of iris pigmentation Mongolian Gull Larus (cachinnans) mongolicus at Lake Baikal, Siberia, Russia (redrawn from field sketches of birds in hand) (Pierre Yésou). Source Surfbirds: IDENTIFICATION OF ADULT VEGA GULL: FIELD OBSERVATIONS FROM JAPAN, FEBRUARY 2003 by Chris Gibbins.

In the birds l examined in the hand, the iris was dull yellow (very pale, almost whitish, in some), usually peppered with grey (pale bluish-grey to dark grey-brown) minute spots in variable density over a much variable extent of the iris surface. In some birds, the grey was peppered quite uniformly over the iris, often with a few small aggregations forming dark marks on the overall pale eye. In other cases, dense grey spots formed one or more large dark areas over the eye while sparse spotting left the yellow iris colour showing over the rest of it (figure 2). Eye darkness is not sex related. Pale eyes and dark eyes are found in both males and females and pairing occurs irrespective of the iris colour (of eight pairs, the male had darker eyes than the female in four cases and the female had darker eyes than the male in three cases; the partners of the remaining pair showed similarly coloured eyes).

Such a high variability of iris pigmentation makes it difficult to accurately comment on the eye colour of mongolicus. In a first analysis of 43 birds in the hand, l classified 28% of them as pale eyed, 42% as intermediate and 30% as dark eyed. A more detailed analysis, including two more samples (table 3), showed that nearly one-third was pale eyed while grey spots covered more than half of the iris surface in another third. Really dark-eyed birds, however, accounted for less than 10%.

In the field, colour assessment is less easy. Of 236 adult birds studied through binoculars or telescope, 89% were classified as yellow or yellowish eyed. It thus seems that eyes classified as pale grey in the hand are perceived as yellowish in the field while dark-eyed birds accounted for only 4% in the field sample (not statistically different from the 8% found during the in-hand examination).

TABLE 3 In-hand assessment of dominant iris colour in three samples of adult Mongolian Gulls Larus (cachinnans) mongolicus trapped at nests at Lake Baikal, Siberia, Russia, in May-June 1992 (percentage of sample size).
Remarks:
A = Several colonies.
B = Different colony.

.
Maloye More A
31 May-7 June (%)
Maloye More B
15 June (%)
North-eastern Lake Baikal
26 June (%)
Pooled (%)
Yellow (grey <10%)
28
28
42
29
Yellowish (grey 10-50%)
44
42
8
41
Pale grey (grey >50%)
21
21
33
22
Dark grey
5
9
-
6
Brown
1
-
17
2
Sample (n)
97
43
12
152

Leg colour

Pyzhianov & Tupitchyn (1992) described the high degree of variability of the leg colour at Lake Baikal and in Mongolia. They examined various series of birds in the hand, comparing the leg colour with colour charts. Grey legs accounted for 22-40%, yellow 13-27%, pink 21-46% and flesh 4-10%, while 6-30% of the birds showed mix-coloured legs. The proportion of each colour type varied between colonies and from one year to the other in a given colony. Also, in a proportion of birds, the leg colour showed temporal changes. According to Pyzhjanov (1998), not only the intensity but also the tone of the coloration changes, He hypothesized that these changes are related to external conditions (food composition) and age. It is a largely acknowledged fact that carotine-rich food can enhance the expression of the carotinoid colouring matter in the legs of gulls (cf Lonnberg 1933). Any relation with age, however, remains to be proven.

I examined in the hand the legs and feet of 152 birds of most colonies I visited at Lake Baikal. It readily appeared that the fleshy-pink colour usually was tinged with some yellow pigment over a very variable extent, Yellow was more often found on and around the knee and on the rear leg while webs often were of a deeper pink (one pink-legged bird with orange webs was most unusual). Some birds exhibited either bright pink or yellow (pale to bright, then resembling michahellis) legs but most showed a variable leg colour. This rendered any reference to colour charts rather subjective and I relied on my own assessment when establishing the dominant leg colour in the examined adult birds. Of them, 15.8% had flesh-to-pink legs, 76.3% yellowish-flesh, 5.9% pale yellow and 2% bright yellow.

In the field, the perception of the yellow tinge varies markedly, depending on the light incidence and on whether the legs are wet or not (yellow shows better on wet legs). Even birds which seem to have yellow legs when looked at them with the naked eye occasionally showed pinkish legs through binoculars. The field score nevertheless matched the in-hand results, with almost all 555 birds studied in the field showing ’pale’ (ie, flesh or pink more or less obviously admixed with yellow) legs and only seven (1.3%) yellow legs.

Mongolicus 2CY, June 17 2013, Lake Ugii, Mongolia (Hadoram Shirihai). Halfway complete moult, P6-P10 still old juvenile. Central MC just replaced, central GC missing, exposing the old secondary bases underneath. New scaps are grey. Mongolicus 2CY, June 17 2013, Lake Ugii, Mongolia (Hadoram Shirihai). Halfway complete moult, P6-P10 still old juvenile. Row of MC just replaced, GC very worn. New scaps boldly barred.
Mongolicus adult, June 17 2013, Lake Ugii, Mongolia (Hadoram Shirihai). Full band on P10, small mirror on P9 and full band on P5. Most birds have pale iris and pink legs. Mongolicus adult, June 01 2013, Bulgan Plantation, Dornod, Mongolia (Hadoram Shirihai). Full band on P10, small mirror on P9 and full band on P5 and black on outerweb P4. Most birds have pale iris with limited peppering and pink legs. Complete moult: P1/P3. PMS=3.

Mongolicus adult, June 11 2013, Dornod, Mongolia (Hadoram Shirihai).

Mongolicus adult, July 13 2012, NE Mongolia (Paul Jones).

Mongolicus adult, June 11 2013, Dornod, Mongolia (Hadoram Shirihai). Medium mirror on P10, full sub-terminal band on P10 and medium pale tongue on P10. Only tiny mirror on P9, full band om P5 and black on outerweb of P4. Yellow iris with some speckling, red orbital ring. Mongolicus adult, June 11 2013, Dornod, Mongolia (Hadoram Shirihai). Medium mirror on P10, full sub-terminal band on P10 and medium pale tongue on P1. Smal mirror on P9, full band om P5 and black on outerweb of P4. Whitish yellow iris with some speckling (peppering category: 10-25%).

END OF PART 3

CONTINUE PART 4: DISCUSSION

Larus cachinnans 2CY-4CY UKK L-010265 March 2011 - February 2013, Deponie Pohlsche Heide - Minden, Germany (52°23'05N, 08°46'45E). Picture: Armin Deutsch.
Larus cachinnans 2CY-5CY UKK T-001874 May 2010 - July 2013, Windheim & Deponie Pohlsche Heide - Minden, Germany. Picture: Armin Deutsch.
Larus cachinnans 1CY & 3CY PATN November 2009 & March 2011, Germany & Switzerland. Picture: Armin Deutsch & Picture: Michel Gorgerat.
Larus cachinnans 2cy-3cy PHHA January 2012 - March 2013, Sambre - lock complex Malonne, Namur, Belgium. Picture: Alain de Broyer & Walther Leers.
Larus cachinnans 3CY PHLD March - July 2013, CET Champteussé-sur-Baconne, France. Picture: Alain Fossé.
Larus cachinnans 3CY PHXA February-March 2013, Deponie Pohlsche Heide - Minden, Germany (52°23'05N, 08°46'45E). Picture: Armin Deutsch.
Larus cachinnans 3CY PKCK March-April 2013, Switzerland. Picture: Christopher Plummer & Julien Torre.
Larus cachinnans 3CY PLKX March 12 2014, Noordwijk beach, the Netherlands. Picture: Mars Muusse.
Larus cachinnans? 2CY-3CY 13P3 November 28 2008 & March 13 2009, Deponie Pohlsche Heide - Minden, Germany (52°23'05N, 08°46'45E). Picture: Armin Deutsch.
Larus cachinnans hybrid? 2CY-3CY PLG DN-04520 March 2005 - March 2006, Deponie Pohlsche Heide - Minden, Germany (52°23'05N, 08°46'45E).
Picture: Armin Deutsch.
Larus cachinnans 3CY B= March 15 2013, Amsterdam, the Netherlands. Picture: Lars Buckx.
Larus cachinnans 3cy, March 12 2011, Ashdod, Israel. Picture: Amir Ben Dov.
Larus cachinnans 3cy, March 08 2011, Ashdod, Israel. Picture: Amir Ben Dov.
Larus cachinnans 3cy, March 08 2011, Ashdod, Israel. Picture: Amir Ben Dov.
Larus cachinnans 3cy, March 02 2012, Ashdod, Israel. Picture: Amir Ben Dov.
Larus cachinnans 3cy, March 08 2011, Ashdod, Israel. Picture: Amir Ben Dov.
Larus cachinnans 3cy, March 08 2011, Ashdod, Israel. Picture: Amir Ben Dov.
Larus cachinnans 3cy, 14 March 2012, Texel, the Netherlands. Picture: Herman Bouman.
Larus cachinnans 3cy, 14 March 2012, Texel, the Netherlands. Picture: Herman Bouman.
Larus cachinnans 3CY, March 15 2013, Amsterdam, the Netherlands. Picture: Lars Buckx.
Larus cachinnans 3cy, March 29 2013, Ashdod Yavne III, Israel. Picture: Amir Ben Dov.
Larus cachinnans 3cy, March 28 2013, Roermond, the Netherlands. Picture: Theo Muusse.

Larus cachinnans 3CY, March 25 2013, Ashdod, Israel. Picture: Amir Ben Dov.

Larus cachinnans 3CY, March 02 2012, Ashdod, Israel. Picture: Amir Ben Dov.
Larus cachinnans 3cy, March 08 2011, Ashdod, Israel. Picture: Amir Ben Dov.